Watercress, best known for its delightful contribution to egg and mayo or rare roast beef finger sandwiches, cotains 312 per cent of the daily recommended value of vitamin K, which is important for building bones and blood clotting. But, nutrient values were capped "so that any one nutrient would not contribute unduly to the total score".

"The scores can serve as a platform for educating people on the concept of nutrient density," said study author Jennifer Di Noia.

"The rankings provide clarity on the nutrient quality of the different foods and may aid in the selection of more nutrient-dense items within the powerhouse group."

Professor Di Noia acknowledged, however, that some other nutrient-dense foods, like berries and garlic, "may have been overlooked" in the study, published in the journal Preventing Chronic Disease.

This was because of the particular nutrient profiling that the study was based on.

Berries, for instance, are rich in antioxidants and phytochemicals, but "there are no uniform data on food phytochemicals and … recommended intake amounts for these compounds are lacking,” Professor Di Noia told the Washington Post.

On the powerhouse foods list however, red pepper won on the fruit front, followed by pumpkin, tomato and lemon.

"Consistent with a whole-diet approach," Professor Di Noia said, “[Consumption of] all of the items should be encouraged. The rankings may help consumers make nutrient-dense selections within the powerhouse group."

POWERHOUSE FRUIT AND VEGETABLES RANKED ACCORDING TO NUTRIENT DENSITY SCORES